Stain decorated glass-ceramic article

ABSTRACT

A method for producing decorated glass-ceramic articles is disclosed. The method involves contacting a surface of a crystallizable glass with molten tin and thereafter applying to the tin-contacting surface a stain decorating composition. The article is then fired at a temperature such that the glass simultaneously crystallizes and the stain diffuses into the article to form the decoration.

This is a division of application Ser. No. 340,513, filed Mar. 12, 1973,now U.S. Pat. No. 3,852,052.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the production of decorated glass-ceramicarticles.

2. Brief Description of the Prior Art

Glass-ceramics are produced through the controlled crystallization ofglass. A glassforming batch to which a nucleating agent is added isfirst melted and the melt then cooled to form a glass article of thedesired shape. The glass article is then subjected to a crystallizingheat treatment in which the glass is first heated to a temperature inthe vicinity of its annealing point to induce nucleation. The nucleatedarticle is then heated to a higher temperature to cause the growth ofcrystals on the nuclei. The glass-ceramic article is composed ofrelatively uniformly fine-grain crystals dispersed in a glassy matrix,the crystals comprising the predominant portion of the article. Thephysical properties exhibited by the glass-ceramic article normally arevery different from those exhibited by the original glass; the principaldifferences being that the glass-ceramics have greater mechanicalstrength, better thermal shock resistance and lower electricalconductivity, making glass-ceramics useful for dinnerware, cookingsurfaces, electrical insulators and other domestic and technicalapplications. Glass-ceramics have been described in detail in U.S. Pat.No. 2,920,971 to S. D. Stookey.

With the increasing prominance and importance of glass-ceramicmaterials, it has become desirable and necessary to decorate articlesmade from such materials. For example, attractive floral decorations ondinnerware makes the articles more appealing to look at and easier tosell. Also, there is a need to decorate glass-ceramic cooking surfacesto mark the location of heaters under the surface.

The art of decorating ceramic articles in an ancient one, with evidencethat glazing of lustrous decorations onto ceramics was common in thePersian Empire. A variety of ceramic decorating techniques have beendeveloped during the long history of the art. Colorants in the form ofceramic glazes, particularly colored spinels, have been coated ontoglass-ceramic articles, and colorants in the form of stain decoratingcompositions have also been used. Stain decorating compositions aredifferent from the glazes in that in stain decorating the colorantmigrates into the crystal matrix of the glass-ceramic, whereas inglazing the colorant remains on the surface. By far the most populardecorating compositions are the stain decorating compositions. Theceramic glazes have high coefficients of thermal expansion and normallycannot be fired onto low-expansion glass-ceramic bodies without severecrazing and peeling. Stain decorations, on the other hand, in which thecolorant diffuses into the body of the glass-ceramic, are far moredurable.

Application of stain decorating to glass-ceramic is accomplished bymixing a colorant such as platinum resinate with a flux such as abismuth compound and adding the mixture to a vehicle such as an oil,alcohol or water, and then applying this composition to the surface of acrystallizable glass article and firing the article to simultaneouslycrystallize the glass and to fix the color to the surface. Methods fordecorating glass-ceramic articles using colorant stains are described inU.S. Pat. No. 3,266,912 to Murphy and U.S. Pat. No. 3,313,644 toMorrissey.

It has been found in stain decorating glass-ceramics that it isextremely difficult to decorate compositions which are free of arsenicand antimony oxides. Arsenic and antimony oxides have been traditionallyused in glass compositions as fining agents and act to remove entrappedbubbles of glass which have been generated during the melting of thebatch ingredients. However, arsenic and antimony oxides present numerousdisadvantages in melting crystallizable glass compositions.Crystallizable glass compositions require rather high meltingtemperatures on the order of about 200° to 300°F. above the meltingtemperature of conventional soda-lime-silica glass. To reach these highmelting temperatures, it is desirable to supply an electrical source ofheat in addition to the conventional form of heating in which oil or gasstreams are burned above the glass melt and the heat is conveyeddownwardly into the glass mass. The electrical source of heating isdirect resistance heating and involves passing an alternating electriccurrent between electrodes usually made of graphite or molybdenum whichare immersed in the glass melt. Glass compositions containing arsenicand antimony oxides attack the electrodes making electric meltingimpractical for such compositions. Removing arsenic and antimony oxidesfrom the compositions, although solving the electrode problem, createsanother problem in that crystallizable glass compositions free of theoxides cannot be satisfactorily stain decorated. The resultant staindecoration is fuzzy and very faint.

SUMMARY OF THE INVENTION

The invention provides a method for stain decorating a glass-ceramicarticle which has been made from a crystallizable glass compositionwhich is substantially free of arsenic and antimony oxides. The methodinvolves a first contacting of the crystallizable glass with molten tin,preferably by floating the glass on the top of a molten tin bath, for asufficient period of time so that tin will diffuse into thetin-contacting glass surface and preferably for a sufficient period oftime in an enclosed atmosphere so that tin will diffuse into all themajor surfaces. The glass is then separated from the tin and the staindecorating composition containing a colorant is applied to a selectedportion of a surface of the crystallizable glass into which tin hasdiffused. The glass is then heated to a temperature sufficient tosimultaneously crystallize the glass and to cause the colorant topenetrate and to stain decorate the surface of the glass.

DETAILED DESCRIPTION

In carrying out the invention, a batch of glass-making ingredientsconsisting essentially of silica, alumina, lithia and a nucleating agentsuch as titania are first mixed together and thereafter melted todissolve and react various ingredients. Glass compositions suitable forproducing glass-ceramic articles are well known in the art and aredisclosed, for example, in U.S. Pat. No. 2,920,971 to Stookey and U.S.Pat. No. 3,625,718 to Petticrew. The glass compositions are preferablysubstantially free or arsenic and antimony oxides which thereby permitsthe use of electric melting. By substantially free of arsenic andantimony oxide is meant that no arsenic or antimony compounds are addedto the batch ingredients and that any arsenic and antimony oxide whichshould show up in the final glass composition is due to an impuritypresent in the batch ingredients and in all instances will be less than0.02 percent by weight based on total weight of the glass composition.

After the batch glass-making ingredients have been uniformly mixed withone another, the batch is charged, usually on a continuous basis, to afurnace or tank where the glass is melted and fined. The temperaturesfor melting and fining of crystallizable glasses are higher than themelting and fining temperatures of conventional soda-lime-silicaglasses. For example, melting and forming temperatures of crystallizableglass compositions are about 3100°F., whereas conventionalsoda-lime-silica glasses are melted and fined at temperatures of about2700°F.

To homogeneously melt and fine the crystallizable glass compositions ofthis temperature, it has been found desirable to provide an electricmelting source in addition to the usual source of heat in which gasstreams are burned above the glass melt and the heat is conveyeddownwardly into the glass mass. Conventionally, electric melting canbest be used by placing the electrodes through the bottom or sides ofthe tank underneath the melted batch.

Electric melting can, of course, be used as the sole source of heat formelting and fining of the glass, in which case additional electrodeshave to be selectively positioned throughout the tank. However, economicconsiderations indicate that electric melting be used in conjunctionwith the standard convection-type of heating.

After the crystallizable glass has been suitably melted and fined,usually for a period of about 12 to 24 hours, it is shaped by blowing,pressing or rolling. The glass article is then contacted with moltentin. By molten tin is meant a molten tin-containing melt which maycontain other ingredients such as is the case with various tin alloys.The most convenient way of contacting the glass with a moltentin-containing melt is to float the crystallizable glass on the uppersurface of a molten tin or tin alloy bath. The crystallizable glass canbe floated on the molten tin bath in essentially two ways. Preferably,the crystallizable glass is first formed into a shape-retaining articleas described above and then floated on top of a molten tin bath. Thus,for example, the glass could be formed into a continuous ribbon bypassing it between water-cooled rolls as it is discharged from thefurnace such as is disclosed in U.S. Patent application Ser. No.222,627, filed Feb. 1, 1972, by Henry M. Demarest, Jr. now U.S. Pat.No.3,771,984. After the glass has been formed, and while it is stillhot, i.e. at a temperature of about 1,400°-1,600°F., it could then bepassed onto a molten tin bath of annealing. The annealing temperatureshould be controlled so that the glass will not crystallize. Althoughsome nucleation may occur, conditions should be controlled so thatnucleation and crystallization are minimized. This annealing temperatureshould be below the nucleation and crystallization temperatures of theglass. Also, quite obviously, the glass could first be annealed byconventional thermal air treatment in a lehr and then subsequentlycontacted with the molten tin bath. Further, it is within the scope ofthis invention that the necessary contact with the molten tin could beachieved by directly forming the crystallizable glass to ashape-retaining article on the molten tin bath. Techniques for formingglass sheets on the molten tin bath are well known in the art and aredisclosed, for example, in U.S. Pat. No. 3,083,551 to Pilkington.

The crystallizable glass should be contacted with the molten tin bathfor a period of time and at a temperature so that sufficient tin will beincorporated into the glass surface so that the crystallizable glasswill be susceptible to subsequent stain decorating. The length of timethe crystallizable glass has to be in contact with the molten tin toachieve the desired tin concentration and penetration will depend onmany variables, such as the temperature of the tin bath, the percentageof oxygen in the atmosphere, whether the crystallizable glass is formedon a molten tin bath on whether the crystallizable glass is contactedwith molten tin after being formed, and on whether the tin-contacting orthe opposed surface is to be stain decorated. In gneral, the glassshould be contacted with the molten tin at a glass temperature of about1,000°-2,500°F. for at least 2 minutes, and preferably in a reducingatmosphere. Much longer contact times, up to one hour or longer, can beused but are not necessary, although longer contact times should be usedwith lower glass temperatures.

It is estimated based on electron microprobe analysis of variouscrystallizable glass samples which have been contacted with molten tin,that the tin should penetrate at least 5 microns, preferably at least 10microns, into the surface of the glass to make the glass surfacesusceptible to stain decorating.

It has been found in the practice of this invention that it is notnecessary in all cases that the stain decorating composition be appliedto tin-contacting surface of the crystallizable glass. If the glass iscontacted with a molten tin bath in an enclosed environment, such asdisclosed in the aforementioned U.S. Pat. No. 3,083,551 to Pilkington,it is known that tin will penetrate the upper surface of the glass whichis not in contact with the tin. Therefore, this surface would beacceptable for stain decorating as long as it had the requiredconcentration and penetration of tin in the surface. What is necessaryis that tin be diffused into the surface layers of the crystallizableglass to be stain decorated. Whether or not the surface to be decoratedhas been in contact with the molten tin is not the critical factor.

After the glass has been contacted with the tin for a sufficient periodof time to achieve the proper penetration and concentration, the glassis separated from the tin bath and made ready for stain decorating.

The stain decorating is accomplished by applying to a selected portionof the tin-contacting surface of the glass the stain decoratingcomposition. The stain decorating composition comprises a coloring agentand, optionally, a fluxing agent dissolved in an oil base. In addition,a diluent to improve the uniformity of the resultant coloration mayoptionally be used. The coloring agents are preferably selected from theprecious metals, such as platinum, palladium, silver and gold.

Decorating compositions containing platinum for use on glass-ceramicsare known in the art and have been described in Chemnitius Spechsaal60,226 (1927); such compositions contain a platinum resinate prepared bycausing a platinum salt to react with a sulfurized terpene such assulfurized Venetian terpene. The platinum resinate is dissolved invehicles such as oils of lavender, rosemary, aniseed, sassafras,wintergreen and fennel, turpentine, various terpenes, nitrobenzene andthe like. Other platinum-containing decorating compositions areplatinums containing halogeno, platinous mercaptide-alkyl sulfidecomplexes such as are described in U.S. Pat. No. 3,022,177 to Fitch.

It is well known in the art that a palladium compound may be prepared inthe same manner as the above-mentioned platinum resinate. Otherpalladium-containing decorating compositions are the bis-thioetherpalladious salt coordination compounds which are described in U.S. Pat.No. 3,216,834 to Fitch.

Besides a colorant, a fluxing agent such as resinates of bismuth orchromium may optionally be used in the staining composition. Thefunction of the fluxing agent is not completely understood in the staindecorating art, although their presence is supposed to improve theappearance of the decoration.

The above-recited glass coloring agents may be used in concentrated formor they may be diluted by mixing them with an inert powder such as TiO₂and ZrO₂. Uniform coloration may be obtained with amounts of diluent upto about 90 percent by weight based on weight of the colorant plusdiluent, but intensity of color diminishes with the higher percentage ofdiluent.

The staining composition is usually applied to a portion of the surfaceof the crystallizable glass by any suitable means or procedure whichproduces an even, uniform coating, such as by spraying, brushing orscreen stenciling. Of the several methods available for applyingdecorations to glass, screen stenciling is preferred. Decoratingscreens, made of 230 mesh perlon, supported in wooden frames can beplaced over the glass and the decorating material placed on the screen.A rubber or plastic squeegee is pulled across the screen, forcing thedecorating material through the screen openings and into the glasssurface. Spacer blocks should be placed under the screen frame so thatthe screen falls within three-sixteenths of an inch from the glass whenit is over the glass. If the screen is too close or too far from theglass, poor decorations will result. The decorating composition must beof the correct viscosity for good screening, about 50,000 centipoises(20°C.). If the material is too thick, a thinner, such as pine oil, canbe added to reduce the viscosity. After the decorating composition hasbeen screen stenciled onto the glass, the glass is air dried at roomtemperature for about 30 minutes before the crystallizing heattreatment, which involves heating the article to a temperature tosimultaneously crystallize the glass and to cause the colorant topenetrate the surface of the glass in the portion where the staindecorating composition was applied.

For the heat treatment, the decorated article is normally placed in anoven, kiln or the like and the temperature steadily raised over a periodof about 3-4 hours from about room temperature to about 1,300°F. Thetemperature is maintained at about 1,300-1,325°F. for approximately 8hours to initiate nucleation of crystallization sites within the glassybody of the article being treated. The temperature is then raised at therate of about 75°F. per hour to about 1,850°F. and held there for about3-4 hours to cause the glass to crystallize throughout the body of thearticle and to simultaneously integrate the colorant and the flux intothe crystalline matrix. The temperature is then reduced as rapidly aspossible consistent with avoiding damage to the refractories andstructural members of the heating chamber. After the article is cooled,a slight residue of the diluent is removed and the article is cleaned.

The resulting decorated article should be opaque and milky white. Thedecoration should be uniform in appearance and a sharp demarkationbetween the areas colored by the decoration and the white body of theglass-ceramic should be apparent. The depth of coloration should be atleast about 1 mil and has been found to be in the range of 1 to 40 milsas determined by cutting through the stain decoration and measuring thedepth of the stain with a measuring eyepiece such as a 50X microscope.

In carrying out the invention, it should be realized that the decoratingcomposition should be applied to the glass body before it has beencrystallized, because crystallization of the glass and coloration of thesemi-crystalline body are thereby accomplished at the same time.

DESCRIPTION OF THE PREFERRED EMBODIMENT

To a commercial-size glass tank capable of containing about 35 tons ofmolten glass and designed for continuous melting and forming are addedon a continuous basis at the feed end of the tank the followingwell-mixed batch ingredients which were free of arsenic and antimonyoxides.

    ______________________________________                                         Ingredient       Parts by Weight                                             ______________________________________                                        Silica            700                                                         Hydrated alumina  296                                                         Lithium carbonate 83                                                          Zinc zirconium silicate                                                                         31                                                          Zinc oxide        10.5                                                        Titanium dioxide  15.0                                                        Lithium fluoride  13.5                                                        Soda ash          4.0                                                         Lithium sulfate   6.0                                                         Potassium carbonate                                                                             2.5                                                                           1161.5                                                      Cullet.sup.(1)    1360                                                        ______________________________________                                         .sup.(1) The glass cullet has the following composition, expressed as         percent by weight: Na.sub.2 O, 0.31%; Li.sub.2 O, 4.13%; F.sup.-, 0.27%;      SiO.sub.2, 70.92%; Al.sub.2 O.sub.3, 19.46%; ZrO.sub.2, 1.54%; ZnO, 1.53%     Fe.sub.2 O.sub.3, 0.05%; TiO.sub.2, 1.56% and K.sub.2 O, 0.18%.          

The glass batch is melted and fined for about 8 hours at a temperatureof about 3,200°F. (melting zone) to 2,900°F. (fining zone). In themelting zone, molybdenum electrodes, extending through the sides andbottom of the tank, are positioned under the melted batch. Theseelectrodes provide a booster source of heat to the hot flames combustionproducts which pass through ports opening into the melting tank abovethe level of glass. The molten glass is removed from the tank at theworking zone at a temperature of 2,600°F. The molten glass is thencontinuously formed between a pair of heavy cast iron, water-cooledrolls. As the glass passes from the water-cooled forming rolls, thesurfaces have become sufficiently chilled to form a more or lessself-sustaining sheet or ribbon, even though the body of the glass isstill very hot.

The formed sheet then enters the annealing lehr at a temperature ofabout 1,500°F. Consequently, in this area, the glass loses heat rapidlyand the temperature falls from about 2,300°F. The annealing lehr isessentially an enclosed molten tin bath which is under a reducingatmosphere of 95 percent nitrogen and 5 percent hydrogen gas. Thetemperature of the lehr is maintained by the heat loss of the glass andconvection heaters and is graduated, being about 1,500°F. at theentrance and tapering to about 95°F. at the end. The overall length ofthe lehr is about 400 feet. Because the glass is less dense than themolten tin, it floats on top of the tin bath.

After annealing, the glass is rapidly cooled to room temperature andremoved from the lehr, inspected and cut to size. The glass at thisstage should have a thickness of about 0.2 inch and have the followingcomposition (exclusive of tin) as determined by wet chemical analysisand X-ray fluorescence.

    ______________________________________                                         Component    Percent by Weight                                               ______________________________________                                        SiO.sub.2    70.67                                                            Al.sub.2 O.sub.3                                                                           19.39                                                            Li.sub.2 O   4.13                                                             TiO.sub.2    1.56                                                             ZrO.sub.2    1.54                                                             Zno          1.53                                                             Na.sub.2 O   0.31                                                             K.sub.2 O    0.18                                                             F.sup.-      0.27                                                             ______________________________________                                    

Electron microprobe analysis should indicate that the tin is principallylocated in the tin-contacting surface of the glass. The tin should havepenetrated to the extent of at least 5 mils into the surface of theglass.

After the glass was annealed on the tin bath, it was inspected, cut tokitchen range top size and set aside for stain decoration.

A stain decorating composition comprising 50 grams of a colorant andcolorant modifier which is known in the art as "dark brown" A-1454 andavailable from Engelhard Industries Inc. containing 2.26 weight percentpalladium and 0.42 weight percent bismuth dissolved in an essential oilis mixed with 450 grams of titanium dioxide diluent. The mixture ofcolorant and diluent is then further mixed with pine oil to make a pastehaving a volume of about 1 pint. The paste is mixed in a roller mill,running through about 3 times. Additional pine oil is mixed into thepaste until the viscosity is about 50,000 centipoises.

A screen made of 230 mesh perlon supported on a wooden frame and havingan open floral design was then placed on the tin-contacting surface ofthe crystallizable glass article to locate the burner areas. Spacerswere placed under the frame to space the screen about three-sixteenthsof an inch from the crystallizable glass surface. The open design of thescreen is sized to compensate for shrinkage of the crystallizable glassduring heat treatment. The decorating paste as described above is placedon the screen, and a polyurethane squeegee is drawn across the screenforcing the paste through the screen openings onto the crystallizableglass. The paste, in its decorative configuration on the crystallizableglass article, is then air dried for about 30 minutes. While drying isnot absolutely necessary, it is done to eliminate any stickiness thatcould result in dirt adherence to the design while placing the articlein the heat treatment chamber. The article is then heat treated tocrystallize the glass-ceramic and to integrate the colorant into thecrystal matrix of the resultant glass-ceramic article.

For heat treating, the glass is stored on racks or the like and put intoa kiln. The temperature of the kiln is raised from room temperature to1,325°F. (nucleation temperature) over the period of 3 hours and held atthis temperature for 8 hours. The glass is then slowly heated at a rateof about75°F. per hour to a temperature of about 1850°F. and held atthis temperature for 4 hours. The kiln temperature is then lowered at arate of 150°F. per hour to 1,300°F. and then the kiln is slowly cooledto room temperature. The glass is removed from the kiln and inspected.Upon visual inspection, the glass should be opaque in appearance and thedecoration dark gray with well defined edges. X-ray diffraction analysisshould indicate that the glass has crystallized to about 95 percentbeta-spodumene solid solution. The palladium stain should havepenetrated to a depth of about 8 mils into the glass-ceramic surface,and a slight residue of TiO₂ should appear on the glass surface.

The durability of the coloration should be excellent as determined by:

a. 100 rubs with a household cleaning powder,

b. 25 rubs with a gold eraser,

c. 25 rubs with an aluminum bar,

d. 3,000 revolutions with a taber abraser-CS-10F calibrate wheel

e. 15 minutes contact 10 percent citric acid

f. 15 minutes contact 10 percent sulfuric acid

g. 15 minutes contact 10 percent sodium hydroxide

h. firing at 1,300°F. for 16 hours with cooking oil in contact

i. heating at 1,300°F. maintained for 168 hours.

No change in design color or quality should be observed except somelightening associated with the taber abraser test. Upon repeating theabove experiment, but without annealing on a molten tin bath, butannealing in a conventional gas-fed lehr, no stain decoration would beobtained.

EXAMPLES I TO IX

The following examples show the effect of various staining compositionson arsenic and antimony-free crystallizable glasses which have, and havenot, been floated on a tin bath. For a control, a crystallizable glasscontaining antimony oxide was also evaluated for staining. The controlglass (Glass C) had the following composition, on an oxide basis:

    Component    Percent by Weight                                                ______________________________________                                        Na.sub.2 O   0.29                                                             Li.sub.2 O   4.05                                                             F.sup.-      0.24                                                             SiO.sub.2    70.84                                                            Al.sub.2 O.sub.3                                                                           19.45                                                            ZrO.sub.2    1.52                                                             ZnO          1.47                                                             Fe.sub.2 O.sub.3                                                                           0.05                                                             TiO.sub.2    1.58                                                             K.sub.2 O    0.18                                                             As.sub.2 O.sub.3                                                                           0.02                                                             Sb.sub.2 O.sub.3                                                                           0.30                                                             ______________________________________                                    

The arsenic and antimony-free glasses had the following compositions, ona weight basis:

                     Percent by Weight                                            Component         Glass A  Glass B                                            ______________________________________                                        Na.sub.2 O        0.54     0.17                                               Li.sub.2 O        3.82     4.15                                               F.sup.-           0.10     0.22                                               SiO.sub.2         71.07    70.20                                              Al.sub.2 O.sub.3  19.57    18.76                                              ZrO.sub.2         1.48     1.31                                               ZnO               1.74     1.93                                               Fe.sub.2 O.sub.3  0.03     0.04                                               TiO.sub.2         1.54     3.00                                               K.sub.2 O         0.10     0.19                                               As.sub.2 O.sub.3  0.00     0.00                                               Sb.sub.2 O.sub.3  0.01     0.01                                               ______________________________________                                    

Three button-shaped glass samples, one of each composition, each havinga diameter of about 21/2 inches and a thickness of about 0.35 inch, weretreated with various stain decorating compositions without firstcontacting the glass samples with molten tin. The stain decoratingcompositions were prepared as follows:StainingComposition Coloring AgentParts by Parts byNo. (Resinate) Weight DiluentWeight______________________________________1 Palladium 5 TiO₂ 952Platinum 5 TiO₂ 953 Gold 5 TiO₂ 954 Silver 5 TiO₂ 955 Nickel 10 TiO₂ 906Cobalt 10 TiO₂ 907 Copper 10 TiO₂ 908 Iron 15 TiO₂ 859 Chromium 15 TiO₂85______________________________________

The coloring agents were mixed with pine oil to form a paste having aviscosity of about 50,000 centipoises at 20°C. The paste was thenapplied to the various glass samples with a brush in the form of a fineline. In all, nine lines, one representing each staining composition,was applied to each of the glass samples.

After the stain decorating compositions were applied to thecrystallizable glass samples, the glass was air dried for 30 minutes andthen put in an oven for a crystallizing heat treatment. Thecrystallizing heat treatment was conducted for the time and temperaturedescribed above in the preferred embodiment of the invention. The glasswas then removed from the oven and inspected. Upon visual inspection,all the glass samples were found to be opaque in appearance and uponX-ray diffraction analysis, were found to be crystallized to at least 95percent by weight beta-spodumene solid solution. The results of thestain decorations are reported in Table I below.

                  Table I                                                         ______________________________________                                        Stain Decoration Results on Arsenic and Antimony-Free Glasses                 Staining                                                                      Composition                                                                            Stain Decoration                                                     No.      Glass A     Glass B     Control                                      ______________________________________                                        1 (Pd)   no decoration                                                                             no decoration                                                                             dark gray                                                                     decoration                                   2 (Pt)   do.         do.         do.                                          3 (Au)   do.         do.         no decoration                                4 (Ag)   do.         do.         do.                                          5 (Ni)   light gray  light gray  light gray                                            decoration  decoration  decoration                                   6 (Co)   dark blue   dark blue   dark blue                                             decoration  decoration  decoration                                   7 (Cu)   no decoration                                                                             no decoration                                                                             no decoration                                8 (Fe)   do.         do.         do.                                          9 (Cr)   do.         do.         do.                                          ______________________________________                                    

The depth of the stains ranged from 1 mil for the light gray nickelstain to 34 mils for the dark gray platinum stain.

The above series of experiments were repeated to samples A and B withthe exception that the samples were first floated on a molten tin bathbefore the staining compositions were applied. In each of theseexperiments, a flat disc of solid tin having a diameter of about 31/2inches and a thickness of about three-fourths of an inch was placed inthe bottom of a 4 inch diameter lavasil crucible. A piece of glasshaving a weight of about 40 grams was placed on top of the tin and a21/2 inch carbon ring was also placed on top of the tin surrounding theglass piece. The purpose of the carbon ring was to prevent the glassupon heating from flowing beyond the confines of the ring and contactingthe sides of the lavasil crucible. After the glass and the carbon ringwere in place, the crucible was purged with a 95:5 mixture of nitrogenand hydrogen gas at a rate of about 10 cubic feet per hour to create areducing atmosphere in the crucible. The crucible, with continuedpurging, was then inserted in a furnace which was preheated to atemperature of about 2550°F. The crucible was contained in the ovenuntil the temperature inside the crucible reached about 2350°F. At thistemperature the tin became molten and the glass sample liquifiedsomewhat and flowed upon the molten tin until it contacted the carbonring. The samples were contained in the furnace for an additional 14minutes at a furnace temperature of 2550°F. The crucible was thenremoved from the furnace and slowly cooled to room temperature whilecontinuously purging with the reducing gas. The glass sample was thenremoved from the crucible and coated with the various stain decoratingcompositions as described above on both the tin-contacting (lower) andupper surfaces. After the stain decorating composition was applied tothe crystallizable glass samples, the coated glass was air dried for 30minutes and put in an oven for a crystallizing heat treatment. Thecrystallizing heat treatment was conducted for the time and temperaturedescribed above in the preferred embodiment of the invention. The glasswas then removed from the oven and inspected. Upon visual inspection,all the glass samples were found to be opaque in appearance and uponX-ray diffraction analysis, were found to be crystallized to at least 95percent by weight beta-spodumene solid solution. The results of thestain decorations are reported in Table II below.

                                      Table II                                    __________________________________________________________________________    Stain Decoration Results on Arsenic and Antimony-Free                         Glasses Which Have Been Floated on a Molten Tin Bath                                 Stain Decoration                                                              Glass A          Glass B                                               Staining                                                                             Bottom or        Bottom or                                             Composition                                                                          Tin-Contacting   Tin-Contacting                                        No.    Surface  Top Surface                                                                           Surface  Top Surface                                  __________________________________________________________________________    (Pd)   dark gray                                                                              dark gray                                                                             dark gray                                                                              dark gray                                           decoration                                                                             decoration                                                                            decoration                                                                             decoration                                   2 (Pt) do.      do.     do.      do.                                          3 (Au) dark brown                                                                             dark brown                                                                            dark brown                                                                             dark brown                                          decoration                                                                             decoration                                                                            decoration                                                                             decoration                                   4 (Ag) dark gray                                                                              light gray                                                                            dark gray                                                                              light gray                                          decoration                                                                             decoration                                                                            decoration                                                                             decoration                                   5 (Ni) light gray                                                                             do.     light gray                                                                             do.                                                 decoration       decoration                                            6 (Co) dark blue                                                                              dark blue                                                                             dark blue                                                                              dark blue                                           decoration                                                                             decoration                                                                            decoration                                                                             decoration                                   7 (Cu) no decoration                                                                          no decoration                                                                         no decoration                                                                          no decoration                                8 (Fe) do.      do.     do.      do.                                          9 (Cr) do.      do.     do.      do.                                          __________________________________________________________________________

In the above results, the depth of penetration of the darker stains wasabout 5 to 20 mils and the lighter stains about 1 to 10 mils.

I claim:
 1. A stain-decorated glass-ceramic article comprising:a solidbody of fine-grain crystals dispersed in a glassy matrix, the crystalsforming the major portion thereof, and including silica, alumina,lithia, and a crystal-nucleating agent, but substantially free ofarsenic and antimony oxides; a tin-penetrated zone extending into saidbody at least 5 microns from at least one surface of said body and inwhich the tin ion concentration is greater than that in interiorportions of said body; a colorant-penetrated zone extending into saidbody from 1 to 40 mils from portions of said at least one surface ofsaid body and in which the concentration of colorant, selected from thegroup consisting of platinum, palladium, silver, and gold, is greaterthan in interior portions of said body.